Alternators are used in modern automotive vehicles to charge the battery and power the electrical system when the vehicle is running. Alternators are typically part of a front end accessory drive system of the vehicle and are often driven by a crankshaft of an associated engine via a belt. An example of a conventional alternator 10 having a fixed pulley 14 coupled to a shaft 18 is shown in FIG. 1. One recognized drawback of conventional alternators is that their rotational speed is directly proportional to the engine speed. Thus the current output of such alternators varies proportional to engine speed, with the rated maximum current output of the alternator being at a normal operating range of the alternator. Such a normal operating range for a motor vehicle alternator is typically between 2500-3500 engine RPM. Therefore, the current output of a typical automotive alternator is less at an engine idle condition, such as 500-700 RPM, as compared to the normal operating range of the alternator.
As a result, automotive vehicle alternators need to be sized to handle the vehicle's maximum anticipated electrical load or current draw at an engine idle condition. Thus, the alternator's current output at an engine idle condition is often the driving factor in determining an appropriate alternator size (i.e., maximum current output) because the alternator's current output at idle is proportional to its rated output at the normal operating range. One drawback of this alternator sizing approach is that the alternator will typically have a larger current output at the normal operating range than is required to handle the vehicle's electrical load at the normal operating range. Such an alternator sized with this approach can be more expensive due to its larger capacity and, in certain operating ranges, less efficient.
Thus, while known alternators with fixed pulleys work for their intended purpose, there remains a need for continuous improvement in the relevant art.